Finding the Pathways to a Cause of Tinnitus

Researchers say they have found a biological explanation for tinnitus, a phantom ringing sound in the ears that affects up to 20% of the general population but isn't well understood.

The underlying cause of tinnitus may be the suppression, or inhibition, of key neural pathways in the brain, according to a report in the Proceedings of the National Academy of Sciences. Past research has shown that tinnitus sufferers have hyperactive auditory circuits but it isn't clear why.

In this study, U.S. researchers subjected normal-hearing mice and mice with induced tinnitus to a sudden loud sound, called a startle test, and measured their response to an unexpected gap in the noise frequency. A technique called flavoprotein autofluorescence was used to image a part of their brain called the dorsal cochlear nucleus (DCN), which is associated with tinnitus. The tinnitus mice showed less inhibition of their startle response than the control mice, causing a hypersensitivity to noise, researchers said. This suggests the DCN is blocked or inhibited in tinnitus, they said. The findings add to scientific understanding of the auditory circuit and cellular changes associated with chronic tinnitus, they said.

Caveat: The experiments were carried out in mice and have yet to be tested in humans. Tinnitus was induced in mice and didn't occur naturally.

Heart attacks do more damage to heart muscle between 6 a.m. and noon than any other time of the day.
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Biological clock of heart attacks: Heart attacks that occur between 6 a.m. and noon cause 20% more damage to heart muscle than attacks at any other time of the day, according to a study published in the journal Heart. The finding suggests there may be natural mechanisms that better protect the heart at other times of the day.

Studies show that heart attacks, including fatal attacks, happen more often in the early morning. A circadian variation in heart-attack size has been found in mice. A study of 811 men and women in Spain who suffered heart attacks from 2003 to 2009 found that peak concentrations of two enzymes released during attacks—creatine kinase and troponin-l, which are indicators of heart-attack size—were 18.3% and 24.6% higher, respectively, during the dark-to-light transition period of the day compared with other times.

More serious anterior wall attacks also occurred during this period. Of the subjects, 269 had heart attacks between 6 a.m. and noon; 240 between noon and 6 p.m.; 161 between 6 p.m. and midnight; and 141 between midnight and 6 a.m. Fluctuations in adrenaline, cortisol, arterial flow and other factors may help to protect the heart during certain times of the day, researchers said.

Caveat: There was no direct evaluation of heart-attack size using magnetic resonance imaging or myocardial scintigraphy, a nuclear imaging test that evaluates the integrity of sympathetic nerves supplying the heart.

Easing IBS: A cooling compound found in peppermint eased the symptoms of irritable bowel syndrome in mice by desensitizing nerve fibers in the large intestine, according to a study in the journal Pain. Irritable bowel syndrome (IBS) is a painful condition that disrupts normal bowel function in about 20% of the general population. Herbal remedies containing peppermint have been shown to significantly reduce bowel hypersensitivity, but the underlying mechanisms are unclear. Australian researchers tested icilin, a potent cooling agent in peppermint, on a sensory pathway called transient receptor potential ion channel melastatin subtype 8 (TRPM8), found in the colon and other parts of the body. Icilin significantly reduced neural activity in colonic fibers in mice exposed to capsaicin, a substance found in spicy foods such as chili and mustard that are believed to trigger IBS. Researchers believe TRPM8 provides a channel that allows icilin to reduce colonic inflammation. TRPM8 may also cross-desensitize other pain-regulating receptors on nerve cells. Herbal remedies or drugs that activate the TRPM8 pathway could have significant therapeutic benefit, they said.

Second-hand smoke and pregnancy: Exposure to second-hand smoke during pregnancy doubles a woman's chances of having a stillbirth.

Babies born to smoke-exposed women also have slightly smaller heads and lower birthweights than those born to mothers from smoke-free environments, according to a study in BJOG: An International Journal of Obstetrics and Gynaecology.

Second-hand smoke, which is thought to expose people to about 1% of the smoke inhaled by smokers, has previously been shown to be associated with cancer, asthma and other serious health conditions in both adults and children. Its effect on pregnancy outcomes was examined in a study of 11,852 Canadian women who gave birth between 2001 and 2009. Subjects included 1,202 (11.1%) women exposed to smoke and 10,650 (89.9%) not exposed. In the exposed group, 7.4% gave birth to babies weighing fewer than 5 pounds, 8 ounces compared with 4.6% in nonexposed mothers. The stillbirth rate was 0.83% and 0.37% in exposed and nonexposed women, respectively.

Exposure also increased prematurity: Of the babies born to smoke-exposed women, 10.2% were born before 37 weeks compared with 8.2% in nonexposed women. Smoke-exposed women also had longer hospital stays. Second-hand smoke may reduce fetal oxygen supply and interfere with nutritional processes, researchers said.

Caveat: Exposure to second-hand smoke was self-reported by women and not verified by researchers. The study didn't attempt to quantify smoke exposure in women. The effect of second-hand smoke on miscarriage rates also isn't known.

Probiotics and UTIs: Suppositories containing probiotics and a type of bacteria that protects against urinary-tract infections reduced urinary-tract infections by 50% in women susceptible to the infection, according to a study in Clinical Infectious Diseases.

Recurrent UTIs affect 30% of women but are increasingly difficult to treat due to growing antibiotic resistance. From 2006 to 2009, antibiotics and probiotic vaginal suppositories were tested in a study of 100 women aged 18 to 40 with frequent UTIs. After an initial course of antibiotics, 50 women were randomly assigned to probiotic suppositories and 50 to placebo suppositories.

The probiotic suppositories contained a strain of Lactobacillus crispatus; depletion of L. crispatus is associated with UTI risk. Both groups were treated for five days and then once a week for 10 days. Results showed that seven of the women using the probiotic suppository had at least one UTI during the study compared with 13 of the placebo group. Larger studies of probiotic suppositories are recommended.

Caveat: Adverse effects were reported by 56% of women in the probiotic group and 50% in the placebo group. The most common were vaginal discharge, itching and abdominal discomfort. One woman in the placebo group discontinued treatment.

Liposuction and fat redistribution: Fat removed from the abdomen, hips and thighs by liposuction, a popular cosmetic surgery, accumulates again within a year to the upper abdomen, shoulders and arms of healthy, nonobese women, according to a study in Obesity.

An estimated 8.5 million liposuction procedures are performed world-wide every year. Although the effects are believed to be permanent, animal studies have shown that fat returns within weeks. This study compared fat redistribution in 14 U.S. women who underwent cosmetic liposuction and 18 controls who didn't have surgery.

Both groups maintained a moderately active lifestyle during the study. At six weeks, body fat decreased by 2.1% in the liposuction group and by 0.28% in the controls; the difference was narrower at six months. At a year, body-fat reduction was 0.41% from before the procedure in the liposuction group but the areas where fat had been surgically removed were unaffected; body fat increased by 0.59% in the controls. Fat redistribution was determined by MRI, X-ray and skinfold measurements.

The study, the first to examine fat redistribution following liposuction, suggests a change in body mass stimulates neurohormonal signals which promote a return to the original weight, researchers said.

Caveat: Because the study was small, it is possible that certain important variables were overlooked that might have affected the outcome, researchers said.

Thyroid and fractures: A common thyroid medication when taken in medium or high doses may increase the risk of fractures in seniors over 70 years old, according to a study in the British Medical Journal. One in five older people take levothyroxine for hypothyroidism, an underproduction of thyroid hormone that occurs with aging. Although patients on the drug are usually monitored, the dose is rarely changed. This study examined levothyroxine doses and risk of fractures in 213,511 Canadians from 2002 to 2007. The average age of subjects was 82; 90% were women. Levothyroxine doses were classed as low, medium or high. The fracture rate during the five years was 10.4%. Risk of fractures—including hip fractures, which have a higher mortality rate—was 3.5 times higher for subjects on high doses of levothyroxine than those on low doses. Risk was 2.5 times higher for those on medium doses than the low-dose subjects. Researchers said high doses of levothyroxine could lead to hyperthyroidism, an excess of thyroid hormone, which can affect bone density. It can also cause heart arrhythmias and muscle weakness, contributing to falls. Levothyroxine doses may need modifying in the elderly, they said.

Caveat: Researchers were unable to measure some factors that might affect the association between levothyroxine and fracture risk, including body mass index, family history, smoking, caffeine or alcohol use and nonprescription drug use. Laboratory confirmation of thyroid-stimulating hormone levels wasn't available.

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